1. Field of the Invention
The present invention relates to an apparatus and method for controlling the amount of flash emission in a camera having a plurality of focus detecting areas.
2. Description of Related Art
In a conventional camera, the relationship between a plurality of focus detecting areas and a plurality of light adjusting sensors (flash light amount detecting means) for detecting amounts of flash light incident on a photographing image plane is made, for example, as shown in FIG. 12. That is, a light adjusting sensor unit composed of three separately provided light adjusting sensors has three light amount detectable areas A', B' and C' respectively serving as the light adjusting sensors, with focus detecting areas SL, SC and SR being respectively located within the central sections of the light amount detectable areas A', B' and C' which can provide the maximum detection sensitivity. In each of the light amount detectable areas, the sensor sensitivity successively decreases as the distance from the central sections increases, and points on each of the curves LA1 to LA5 in each of the light amount detectable areas A', B' and C' have the same sensor sensitivity.
Furthermore, in the above camera, an in-focus area can be selectively set from the plurality of focus detecting areas SL, SC and SR, and the light adjusting sensor having the light amount detectable area including the selectively set in-focus area is chosen to determine a target detected amount of received light by the selected light adjusting sensor on the basis of a film ISO sensitivity, an aperture value or the like. On the other hand, in terms of the light adjusting sensors each having the light amount detectable area not including the in-focus area, the correction of the target detected amount of received light takes place to equally exceed the aforesaid target detected amount of received light by a given or predetermined value.
For instance, in the case of focusing in the focus detecting area SC being at the central position, a decision is made that there is a person or subject in the central location, and a method to mainly weight the central sensor B is taken so that this central location provides an appropriate light emission amount. Thus, as shown in FIG. 13, the correction amount "0 step" for the target detected amount of received light is set with respect to the sensor B, whereas the correction amount "+1.0 step" for the target detected amount of received light is set with respect to the sensors A and C, respectively.
The correction amount "0 step" set for the sensor B signifies that the target detected amount of received light is set through the use of a value directly calculated on the basis of the film ISO sensitivity, the aperture value or the like, and the correction amount "+1.0 step" to be set for the sensors A and C means that the target detected amount of received light is set to exceed that amount by +1.0 step. This is for the purpose of, in the case of bringing a central subject into focus and of photographing the central subject with a proper flash light amount and in a scene where the central subject is considerably remote and an object exists at a left or right position closer than the central subject, preventing the left or right object from abnormally resulting in an overexposure.
Likewise, in the case of focusing in the left focus detecting area SL, the weighting is done with the correction amount "0 step" with respect to the sensor A while being done with the correction amount "+1.0 step" with respect to the sensors B and C. On the other hand, in the case of focusing in the right focus detecting area SR, the weighting based on the correction amount "0 step" takes place with respect to the sensor C while the weighting by the correction amount "+1.0 step" is done for the sensors A and B.
After the target detected amounts of received light are thus set for the respective light adjusting sensors, the flash light emission takes place, and when the detected amount of received light for one of the light adjusting sensors reaches the target detected amount of received light set for that light adjusting sensor, the flash light emission is put to an end.
In the case where, like the example of FIG. 12, the number of focus detecting areas is relatively small and they are in one-to-one corresponding relation to the light amount detectable areas (that is, the divisional number of the light adjusting sensors), a need for complicated control does not particularly exist.
However, the latest cameras have a tendency to sharply increase the number of focus detecting areas, and hence, if the number of focus detecting areas is set to equal the divisional number of the light adjusting sensors, the cost for the light adjusting sensors increases.
In addition, the increase in the number of focus detecting areas causes a larger-size of the focus detecting apparatus, which requires that the light adjusting sensors are disposed close to the film surface. What's more, for example, bringing the light adjusting sensors close to the film surface makes a significant difference between the light adjusting sensor sensitivity for the central section of the film surface and the light adjusting sensor sensitivity for the upper and lower sections of the film surface, and therefore, difficulty is encountered to equally accomplish the flash light amount control as mentioned above between the case where the focus detecting area placed in a high-sensitivity section is chosen as the in-focus area and the case where the focus detecting area placed in a low-sensitivity section is selected as the in-focus area.
Furthermore, in a case where the automatic in-focus area selecting function selects a plurality of in-focus areas, since only one in-focus area with a high reliability is extracted from these in-focus areas and the target detected amounts of received light for the light adjusting sensors other than the light adjusting sensor corresponding to the extracted in-focus area are corrected to equally exceed, by a given value, the target detected amount of received light of the light adjusting sensor corresponding to the extracted in-focus area, when all the focus detecting areas are at the low-sensitivity portions of the light adjusting sensors, the overexposure photography occurs similarly.
Still further, the size of the subject and the distance therefrom have great influence in terms of the sensitivity distribution of the light adjusting sensors resulting in large difference in the flash light emission amount, so that there appears a difference among the pictures taken using the flash light emission.